Norway rats (Rattus norvegicus) were introduced to North America in the mid-1700's. They originated from Asia, but arrived on our continent via ships from Europe, where they had been thriving for centuries. Norway rats are sometimes called "brown rats", "sewer rats", "street rats" or "wharf rats". They have a stocky build, weighing about a pound when full-grown (larger than a roof rat), with 12 to 18 inch long bodies. Norway rats generally eat whatever they can find. For example, a balanced diet of meat, fish, grains, and some fruits, often culled from human garbage. However, they will eat just about anything when necessary. When searching for food and water, Norway rats usually travel an area of about 100 to 150 feet in diameter. They seldom travel any further than 300 feet from their burrows or nests. A well known fact is that Norway rats are nocturnal and prefer to come out at night. But what is not widely known is that they don't see well and are color blind.

The average female Norway rat has four to six litters per year and may successfully wean 20 or more offspring annually. Their nests may be lined with shredded paper, cloth, or other fibrous material. Their droppings may be up to an inch long, though usually a bit shorter. A single rat can produce 50 droppings per day. The Norway rat occurs throughout the 48 contiguous United States in Canada and in Mexico. Generally it is founds at lower elevations. They can burrow through cement foundations, causing major damage to buildings by undermining foundations and concrete slabs. They gnaw on just about any material including plastic, wood, and soft metals such as copper and lead. When Norway rats invade buildings, they usually remain within the basement or ground floor, although they can climb. For this reason, they are often called "ground rats".